The effects of CO, water vapor and surface temperature on the conductivity of a SnO2 gas sensor

It is shown that the conductivity of a SnO2 gas sensor depends on the concentration of CO and H2O in the atmosphere n which it is placed. The experimental data can be explained in a consistent manner by hypothesizing that 1) adsorbed oxygen depletes the surface electron concentration and therefore decreases the conductivity; 2) adsorbed water causes electrons to accumulate at the surface and therefore increases the conductivity; 3) CO increases the conductivity by removing adsorbed oxygen by reacting with it to form CO2; and 4) adsorbed water catalyzes the CO to CO2 reaction.